Energy storage elements, such as batteries, may deteriorate under over-temperature conditions. FIG. 1 illustrates a schematic diagram of a conventional over-temperature detection circuit 100. The conventional over-temperature detection circuit 100 includes an integrated circuit (IC) chip 110 and a negative temperature coefficient (NTC) thermistor 130 externally coupled to the chip 110 via a dedicated analog NTC pin. The chip 110 can include a comparator 120 and multiple internal resistors, e.g., a resistor 112, a resistor 114, a resistor 116 and a resistor 118. For example, the internal resistors are integrated onto the IC chip 110. The thermistor 130 can sense temperature of, e.g., a battery pack, and can vary resistance of the thermistor 130 when the temperature changes. A voltage divider constituted by the resistor 118, the resistor 112 and the thermistor 130 provides a temperature sense voltage at node 122. Another voltage divider constituted by the resistor 118, the resistor 114 and the resistor 116 provides a reference threshold voltage indicative of a temperature threshold at node 124. The comparator 120 compares the temperature sense voltage to the reference threshold voltage, and generates an over-temperature detection signal OTA if the temperature sense voltage drops below the reference threshold voltage. Thus, when the temperature reaches the temperature threshold, the resistance of the thermistor 130 depends on the resistance of internal resistors, e.g., the resistors 112, 114, 116.
The internal resistors can be fabricated by a doped region on a silicon chip. Therefore, resistance of the internal resistors varies in different chips or different doped regions of the same chip, which may affect the accuracy of the temperature detection circuit 100. In addition, resistance of the resistor 118 may be set relatively high to reduce the current consumption, which may increase the chip size and the cost of the over-temperature detection circuit 100.
FIG. 2 illustrates a schematic diagram of another conventional over-temperature detection circuit 200. Elements labeled the same as in FIG. 1 have similar functions. The over-temperature detection circuit 200 includes an external adjustable resistor 210 coupled to the thermistor 130 and to the IC chip 110 for adjusting errors caused by the resistance variation of the internal resistors. However, chip size remains an issue.
FIG. 3 illustrates a schematic diagram of another conventional over-temperature detection circuit 300. Elements labeled the same as in FIG. 1 and FIG. 2 have similar functions. The over-temperature detection circuit 300 includes an external resistor 312 in series with the thermistor 130. As such, a temperature sense voltage at node 302 can be provided by a voltage divider including the external resistor 312 and the thermistor 130, and a reference threshold voltage at node 304 can be provided by a voltage divider including resistors 116 and 114. However, a leakage current can flow through the resistor 312 and the thermistor 130 even when the IC chip 310 is powered off, which may increase power consumption.
Resistance of the resistors involved in the conventional over-temperature detection circuits 100, 200, and 300, e.g., the internal resistor 118 and the external resistor 312, can be increased to reduce the power consumption. As a result, the current flowing through the thermistor 130 can be decreased. Thus, when the temperature varies, the corresponding voltage change of the temperature sense voltage at node 302 or 122 can be decreased. By way of example, the temperature may reach the temperature threshold. The temperature sense voltage is then equal to the threshold voltage. If the temperature is increased, the temperature sense voltage can be decreased to less than the threshold voltage. In some circumstances, the voltage change of the temperature sense voltage may be lower than an offset voltage of the comparator 120, or the relatively small voltage change of the temperature sense voltage may be affected by coupling noise of the comparator 120. Thus, the detection signal OTA, e.g., a high electric level, may not be generated to indicate the over-temperature condition. As such, the accuracy of the over-temperature detection circuits 100, 200, and 300 may be degraded.